1. Field of the Invention
The present invention relates generally to shock absorbers for aircraft. More particularly, the present invention relates to gas-actuated shock absorbers for use in the landing gear of pleasure-soaring, or light utility, aircraft.
2. Description of the Prior Art
In the early days of aviation it was common for flying enthusiasts to design and fabricate their own airplanes. Later, kits were available for those who desired to fly but did not have the funds to purchase factory made airplanes; and all through the ensuing years there have been those who have built their own airplanes.
More recently a new class of aircraft has developed which is called "ultralight." Ultralight aircraft started with the bare necessities that would produce flight and carry the pilot and have evolved to a more sophisticated pleasure aircraft. Ultralight airplanes may be purchased completely manufactured or in kit form.
An ultralight airplane may have a wing loading in the vicinity of three pounds per square foot, weigh two hundred and fifty pounds, or so, use an engine of thirty horsepower, or so, have a cruising speed of about sixty miles per hour, and may carry a load, including the pilot, of approximately two hundred pounds.
An even more recent development is a category of aircraft which is intermediate of ultralights and general aviation. Aircraft in this new category weigh fifty to several hundred pounds, more than ultralights, have a cruising speed of ten to seventy miles per hour, or so, more than that of ultralights, and have an engine that has ten to seventy more horsepower than ultralights; and these aircraft will have light utility applications as well as pleasure.
The landing gears of ultralight aircraft have been constructed of a heat-treated material. Little, if any provision has been made to soften landings; although some ultralights have used rubber wrapped around separating members of the landing gear to soften the landings.
There have been several problems with providing shock absorbing struts for ultralights; and the same problems will exhist to almost the same extent with this new, slightly larger, and slightly more expensive type of aircraft.
Ultralights are a pleasure-soaring type of aircraft. They are designed and built for the person who enjoys going up for an hour or two, one or two days a week, when the weather is good.
Since the wing loading is very low, and both the cruising and landing speeds are low, the gust loading is high. Thus, there are many days, in most parts of the world, that the wind is too strong for either ultralights or this new, and slightly larger, aircraft.
Also, with a quite limited cruising speed, it is not practical to attempt to fly long distances; because either a head wind may make ground speed extremely slow; or, by the time the pilot arrives at his destination, the wind velocity may have increased and landing may be hazardous, or flying without instruments and an instrument rating may not be safe.
Therefore, a first problem in designing a shock absorber for these two types of aircraft is that it is necessary to keep the selling price within an acceptable range. Thus, price rules out standard types of aircraft shock absorbers.
A second problem is that of weight combined with price. With all aircraft, weight is a primary concern. However, when it is necessary to consider both weight and cost, the problem intensifies.
One way to eliminate a part of the weight is to eliminate the weight of the oil; and instead, provide an air, or gas, spring, and then also provide shock-absorbing chamber by restricting gas, or air, movement from one chamber to another. Flader, in U.S. Pat. No. 1,528,918, describes such a gas-operated shock absorber for aircraft.
It has been a problem to pressurize aircraft shock struts of the type using a gas charge with oil, and of the type using only a gas. Cautley, in U.S. Pat. No. 2,055,248, disclosed a hand pump for increasing the pressure of air from a standard air compressor to the pressure that is required for the shock strut.
More recently, it has been standard practice to pressurize aircraft shock absorbers with an inert gas from a pressurized bottle.
However, the owner of an ultralight cannot be expected to have either a booster pump, as described by Cautley, or a pressurized bottle of inert gas to service his aircraft.
Thus, the prior art does not teach the construction of a shock absorber that meets the requirements of: low cost, light weight, and low charging pressure.